A compost pile with wet feet will get cold and anaerobic really easy.
If it were me, I would keep the lagoon and set up a lovable loo system next to the flush toilets for as long as you can physically handle it. Use the lagoon when you have to, hopefully never.
Have you seen the home biogas digester? Sort of septic where you capture the methane to cook: https://www.homebiogas.com
Not something I would want to sell to zoning right now, but something to think about--something that SHOULD be the standard.